This invention concerns the use of polyaryletherketone-based thermoplastic materials in downhole logging applications. By way of background, downhole logging tools are exposed to difficult environmental conditions. The average depth of wells drilled each year becomes deeper and deeper, both on land and offshore. As the wells become deeper, the operating pressures and temperatures become higher. The open hole involves the drilling of a borehole through subsurface formations. After the drill bit has passed through each strata, it leaves a fairly rough, abrasive surface along the borehole wall. Wall spalling can also create sharp edges. While the abrasive nature is reduced by the accumulation of mud cake on the borehole wall, the repeated travel of a logging tool through the borehole still produces abrasive wear to the borehole wall. In addition, a deviated borehole will further lead to abrasive wear on the logging tools.
Drilled wells present an extremely hostile environment. Boreholes are often rugose and abrasive. Drilling muds, which are used to facilitate drilling, contain chemical additives that may degrade non-metallic materials. They are highly caustic with a pH ranging as high as 12.5. Other well fluids may include salt water, crude oil, carbon dioxide, and hydrogen sulfide, all of which are corrosive to many materials.
Downhole conditions progressively become more hostile at greater depths. At depths of 5,000 to 8,000 meters, bottom hole temperatures (BHT) of 260.degree. C. and pressures of 170 Mpa are often encountered. This exacerbates degradation of exposed logging tool materials.
These deep well conditions of high pressure and high temperature (hereinafter, "HPHT") damage the external or exposed logging tool components. Internal electronics need to be protected from heat and external housing need to be upgraded. The most vulnerable materials are the plastic and composite materials that are exposed to caustic drilling mud and other corrosive borehole fluids. Some tools, such as those making electrical induction, resistivity, and magnetic resonance measurements, require these non-conductive, non-magnetic materials of construction in order to function properly. This requires materials that are essentially transparent to electromagnetic radiation and have a magnetic permeability of one.
Ceramics generally are too brittle, i.e., a sharp impact may fracture the ceramic. Conventional plastics, such as epoxies and phenolics, perform adequately in conditions up to about 180.degree. C. and 100 Mpa. Under more extreme conditions, however, they fail prematurely. Many alternative materials have been evaluated and rejected for various reasons. For example, polyimides, polyethermide ("ULTEM"), and polyamideimide ("TORLON") are well known for their excellent durability at high temperature. These materials fail in borehole fluids because the -imid and -amide linkages are subject to rapid hydrolytic degradation at high pH. Polyphenylene sulfide is water resistant but its crystalline melting point, 260.degree. C. is too low for HPHT applications.